Diesel engines, some gasoline fueled engines, and many hydrocarbon fueled power plants are operated at higher than stoichiometric air-to-fuel mass ratios for improved fuel economy. Such lean-burning engines and other power sources, however, produce a hot gaseous exhaust with relatively high contents of oxygen, water, and nitrogen oxides (mostly NO and NO2, collectively, NOx). In the case of diesel engines, the temperature of the exhaust gas from a warmed up engine is typically in the range of about 200 degrees to 400 degrees Celsius, and has a representative composition, by volume, of about 10% oxygen, 6% carbon dioxide, 0.1% carbon monoxide (CO), 180 ppm hydrocarbons (HC), 235 ppm NOx and the balance substantially nitrogen and water. The exhaust gas often contains some very small carbon-rich particles. And to the extent that the hydrocarbon fuel contains sulfur, the exhaust from the combustion source may also contain sulfur dioxide. It is desired to treat such exhaust gas compositions to minimize the discharge of any substance to the atmosphere other than nitrogen, carbon dioxide, and water.
The NOx gases, typically comprising varying mixtures of nitrogen oxide (NO) and nitrogen dioxide (NO2), are difficult to reduce to nitrogen (N2) because of the oxygen (O2) content (and water content) in the hot exhaust stream. It is found that when much of the NO is oxidized to NO2, there are selective catalytic reduction additives and reaction methods for reducing much of the NO2 to nitrogen in the hot exhaust. But the effective and timely oxidation of NO (and CO and HC) in the exhaust has required the use of platinum as a catalyst. There is a need for a much less-expensive catalyst material for such oxidation reactions, whether in a combustion exhaust steam or in another gaseous environment.